Achiral organoiodine-functionalized helical polyisocyanides for multiple asymmetric dearomative oxidations

Immobilizing organocatalyst onto helical polymers not only facilitates the catalyst recycling from homogeneous reactions, but also boosts enantioselectivity. In this work, achiral organoiodine-functionalized single left- and right-handed helical polyisocyanides were prepared from the same monomers, which catalyzed three asymmetric oxidations gave the desired products in high yields and excellent enantioselectivity. The enantiomeric excess of the target products was up to 95%. Remarkably, the enantioselectivity can be switched by reversing the helicity of the polymer backbone. The polymer catalysts can be facilely recovered and recycled in different asymmetric oxidations with maintained excellent activity and enantioselectivity.


Supplementary Methods
Measurements. NMR spectra were recorded using a Bruker 600 MHz or 400 MHz spectrometer {H} operated in the Fourier Transform mode. Chemical shifts are reported in delta (δ) units and expressed in parts per million (ppm) downfield from tetramethylsilane (TMS) using the residual solvent proton as an internal standard. Size exclusion chromatography (SEC) was performed on Waters 1515 pump and Waters 2414 differential refractive index (RI) detector (set at 40 °C) using a series of two linear TSK gel GMHHR-H columns. Molecular weight (Mn) and its dispersity (Mw/Mn) data are reported relative to polystyrene standards. The eluent was tetrahydrofuran (THF) at a flow rate of 0.8 mL/min. FT-IR spectra were recorded on Perkin-Elmer Spectrum BX FT-IR system using KBr pellets. CD spectra were obtained in a 1.0 mm quartz cell at 25 °C using a JASCO J1500 spectropolarimeter. Absorption spectra were recorded on UNIC 4802 UV/vis double beam spectrophotometer in a 1.0 cm quartz cell at 25 °C.
The optical rotations were measured in CHCl3 at room temperature using a 10.0 cm quartz cell on a WZZ-2S polarimeter. Matrix assisted laser desorption ionizations with time of flight detection mass spectroscopy (MALDI-TOF MS) measurements were performed on a Bruker Reflex III using dithranol as a matrix and sodium trifluoroacetate as an ion source. High performance liquid chromatography (HPLC) with UV-vis detector was carried out on SHIMADZU LC-20AT equipment using chiral column.
Materials. All solvents were obtained from Sinopharm. Co. Ltd., and were purified by the standard procedures before use. In experiments that required dry solvents, tetrahydrofuran (THF), toluene, chloroform (CHCl3) and dichloromethane (CH2Cl2) were dried using standard methods and distilled before use. All chemicals were purchased from Aladdin, Sinopharm, and Sigma-Aldrich Chemical Co. Ltd., and were used as received otherwise denoted. The 4-methoxy-phenylacetylene Pd(II) catalyst (alkyne-Pd(II)), monomer 1, and the phenyl isocyanide bearing pentafluorophenol ester (16) were prepared following the reported procedures, and the structures were confirmed by 1 H NMR. 1-4 Monomer 2 was prepared according to Scheme S1.

Supplementary Fig. 1 Synthetic Route for Monomer 2
Synthesis of 11. The compound was prepared following the reported literature with modification. 5 Into a solution of 2-amino-3-nitrophenol (3.02 g, 19.6 mmol) in dimethyl sulfoxide (DMSO, 50 mL) was added aq. 30% H2SO4 (100 mL). The mixtures were stirred for 1 h and cooled to 0 °C with an ice-water bath, the mixture was treated with a solution of NaNO2 (1.99 g, 28.7 mmol) in deionized H2O (10 mL) for 15 minutes.

Procedures for asymmetric catalysis:
Compound 3 was prepared according to the reported procedure and the structure was confirmed by 1 H NMR. 6 The compound 3 (4.28 mg, 0.02 mmol) was dissolved in days, the mixture was poured into aqueous solution of Na2S2O3 and NaHCO3 (5 mL).
The aqueous layer was separated and extracted with CH2Cl2 (2 times). The combined organic layers were dried over anhydrous MgSO4 and solvents were removed in vacuo.